OBJECTIVE Resistin is a novel hormone secreted by human adipocytes and mononuclear cells. It is expressed in the human placenta, and has been postulated to play a role in the regulation of energy metabolism during pregnancy. However, correlations between umbilical and maternal serum resistin levels and neonatal birth weight remain poorly understood. The purpose of the study was to clarify the correlation between umbilical cord and maternal serum resistin levels and neonatal birth weight. METHODS This study included 37 healthy mothers, neonates. Resistin levels were determined by ELISA, and compared for correlation between umbilical cord and maternal serum resistin levels and neonatal birth weight. RESULTS The ranges of resistin levels for umbilical and maternal sera were 10.61-40.81 and 1.14-25.54 ng/ml, respectively. Mean umbilical serum resistin level (21.34+/-1.07 ng/ml) was significantly higher than maternal serum resistin level (10.13+/-1.12) (p<0.001). Umbilical serum resistin levels were positively correlated with maternal serum resistin levels (r=0.607, p<0.001) and negatively with neonatal birth weight (r= - 0.345, p=0.037). No significant differences in resistin levels were discovered between the female and male neonates. In addition, there were no correlation between the umbilical resistin levels and maternal body mass indices, umbilical leptin levels, or insulin levels. CONCLUSIONS It is suggested that resistin not only affects energy homeostasis by existing in high levels in the fetus, but may play an important role in controlling body weight through effective regulation of adipogenesis by negative feedback.